Accurate determination of absorbed dose during radiation therapy is extremely important in insuring that the maximum radiation dose is delivered to a cancerous region with minimum damage to surrounding tissue. At present the dose is determined theoretically and verified using thermoluminescent dosimeters (TLD's). However, use of TLD's only provides information about absorbed dose after the patient has been irradiated. Ideally, it would be desirable to have an in vivo dosimeter which is capable of providing real time dose rate information allowing for on-line dose adjustments to maximize the effectiveness of radiotherapy. In order to achieve this goal, applicants are proposing to evaluate the feasibility of fabricating miniature radiation sensor probes using its patented storage phosphor materials. These materials can be attached to the end of a thin optical fiber to produce a miniature sensor suitable for real time in vivo radiation dosimetry.